Weighing and feeding control system



Sept- 18, 1956 E. c. GREGORY WEIGHING AND FEEDING CONTROL SYSTEM 5Sheets-Sheet l Filed Oct. l2, A1953 INVENTOR lien Il.

ATTORNEYS Sept- 18, 1956 E. c. GREGORY 2,763,457

WEIGHING AND FEEDING CONTROL SYSTEM INVENTOR BY ld-73014 ML waZ-sowATTOR NEY Sept- 18, 1956 E. c. GREGORY WEIGHING AND FEEDING CONTROLSYSTEM C5 Sheets-Sheet 3 Filed Oct. l2, 1955 INVENTOR ATTORNEY5 UnitedStates Patent O WEIGHING AND FEEDIN G CONTROL SYSTEM Edwin C. Gregory,Evansville, Ind., assignor to Electronics Research, Inc., Evansville,Ind., a corporation of Indiana This invention relates to apparatus foruse in the weighing, feeding, and packaging of solid material in dividedform, and especially of free flowing powdered or granular material,liquids, slurries and the like, and finds its principal use in thefilling of containers with accurately measured amounts by weight of suchmaterial. It is the primary object of the invention to provide apparatusof the class indicated in which the feeding or pouring into containersof the material in measured amount is effected automatically and withunusual accuracy.

In the preferred embodiment of the invention, hereinafter referred to asthe net weight system, the weight of the empty container is rstdetermined with accuracy, :and due compensation for variation from anaverage or standard weight is effected, preferably by restoring thescale platform to a predetermined position, for instance its initialunloaded position, whereupon a measured amount of material isautomatically fed into the container, the feeding rate being controlledthroughout the feeding cycle in such manner as to insure delivery to thecontainer of a precise predetermined total amount by weight thereof,whereupon feeding is automatically ter- Initiated.

In a further embodiment of the invention, hereinafter referred to as thegross weight system, the determination of the weight of the emptycontainer is omitted, the apparatus being restricted essentially to suchelements as are required for delivery of the material from a source intoa container or onto a scale pan or the like until a predetermined grossweight is established.

A feature of the invention is the establishment of a feeding cycleinvolving (a) the feeding of material at a maximum predetermined rateduring the first and major portion of the cycle, (b) progressive andgradual reduction of the feeding rate to zero during the latter portionof the feeding cycle, and (c) the reinitiation and subsequenttermination of feeding for the purpose of delivering a measured smallquantity of material in the event the total quantity of materialrequired has not been fed prior to such reinitiation of feeding, wherebythe effects of inertia of the moving material and of the moving parts ofthe apparatus are minimized or eliminated. The invention alsocontemplates automatic minor regulation of the rate of feeding of thematerial during any part of the feeding cycle subsequent to the firstand major portion thereof.

Prior art systems for automatic filling of containers usually rely foraccurate measurement of the material on the dribble method ofcontrolling feed, in which nearly all of the material is charged to thecontainer at a fixed maximum rate, the rate of feed being then abruptlyreduced to a constant minimum rate which is terminated when thecontainer weight is approximately correct. However, since the materialcannot be measured accurately while flowing at the maximum rate, owingto variation in operating conditions and in the character of thematerial being fed, dribbling of the final measured amount must beprolonged somewhat to aliow adequate compensation for error in thefeeding at the maximum rate. It can be shown, therefore, that thepresent system, employing a feeding cycle of the character hereinbeforeindicated, results in quicker and more accurate charging of containers,especially when provision is made for continuous coordination of therate of progressive reduction of feed with the weight of material in thecontainer.

A further feature of the invention, in its application to the net weightsystem, is the provision of means whereby the filling of a container isautomatically prevented whenever the weight of the container fallsoutside of predetermined limits, and of means whereby variation ofcontainer weight within such predetermined limits -is detected and dulycompensated, whereby the final weight of the filled container may beused to determine automatically the amount of material charged to thecontainer regardless of minor variation in container weight.

It is a further object of the invention to provide, in an apparatus ofthe general class indicated, an electronic control to effect the feedingof a precise amount of weight of material.

Further objects and features of the invention will be apparent from thefollowing description, taken in connection with the accompanyingdrawings, in which Figure l is a wiring diagram of a net weight systemof the type hereinbefore generally described, embodying the principlesof the invention;

Figure 2 is a diagrammatic representation of certain components of thesystem shown in Figure l, showing mechanical connections therebetween;and

Figure 3 is a wiring diagram of a gross weighing system, correspondinggenerally with the system shown in Figures l and 2, but omittingelements thereof utilized solely for the weighing of empty containersand the compensation for variation in weight thereof.

For the purpose of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawing, and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated apparatus, and such further applicationof the principles of the invention as illustrated therein, beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

Referring first to Figure 2, in which is illustrated in a simple mannerthe physical relationship of certain coniponents of my system, there isshown at a scale platform or weighing pan on which may be placed acontainer 71 to be charged with a measured amount of material. Platform70 is supported on a pedestal 72 which is mounted for substantiallyvertical displacement on a pair of spring beams 75, the beams beinganchored at their opposite ends on an upright support 76 mounted on abase 77, the beams functioning essentially as a parallel linkage,whereby the pedestal 72 is maintained in an upright position, verticaldisplacement of the pedestal in response to a load on platform 70 beingyieldingly resisted by the resilience of the beams. To an arm 78, rigidwith pedestal 72, is secured a bias spring S0, the tension exerted byspring Si) being varied by operation of rebalancing servomotor 82, whichdrives a reel 83 to which the lower end of spring 80 is peripherallyconnected. It will be appreciated that when servomotor 82 is energizedto rotate reel 83 in a counterclockwise direction, the spring 80 isrelaxed and the pedestal 72 and scale platform 70 are permitted to riseproportionately. Operation of motor 82 in a direction to increase thetension of spring 80 tends to depress the platform 70 against the actionof spring beams 75. The structure thus far described is conventional insystems of this character, and

the details thereof form no part of the invention, but may be modifiedas desired. Y

Upon vertical displacement of platform 70 and pedestal 72, the movingelements of each of two weight sensing devices S. 1 and S. 2 arecorrespondingly displaced. To this end, the lower end of pedestal 72 isprovided with laterally extending arms 85 and 86; rods S8 and 89, eachcoupled for displacement with the moving element of one of the weightsensing devices, are adjustably connected in any convenient manner tothese arms. The simple form of adjustable connection shown in thedrawing for the purpose of illustration may, of course, be replaced byequivalent and more complex types of connection, designed to affordaccurate adjustment of the position of the moving elements of thesensing devices corresponding to any given position of the platform 70.Each of the sensing devices may be constituted by a variable irnpedanceof a known type, more specifically, a linearly variable differentialtransformer, such as illustrated by conventional electrical symbols inFigure l, and is so connected in a circuit as to develop a signal ofwhich the absolute value and the phase relationship are determined bythe position of its moving element, whereby the signal output isrepresentative of the position of the scale platform 70, in a mannerreadily understood in the art to which the invention relates. Motor 82and sensing devices S. 1 and S. 2 may be mounted rigidly on base 77.

Scale platform 70 is positioned immediately below a hopper 90, adaptedto receive the material to be charged into the containers 71, the hopperhaving an opening 91 at its lower end which is controlled by a gatevalve 92, supported to slide transversely of the opening. Control meansfor displacing gate valve 92 to control discharge of material fromhopper 90 is schematically shown as comprising crank disk 94 andconnecting rod 95, the latter being pivotally connected to valve 92.Crank disk 94 may be driven by worm 97 which is rotated by control valveservomotor 100. Again it will be appreciated that, in order to simplifythe illustration, an elementary form of driving connection between themotor 100 and the gate valve 92 has'been selected, and that these areconventional detail's which may be modified as desired. A potentiometerR1 is connected for adjustment in response to displacement of gate valve92, for instance by coupling the movable element of the potentiometer todisk 94 by a link 101, whereby the potentiometer resistance is varied asthe position of the valve is altered by energization of servomotor 100.Potentiometer R1 is employed, as hereinafter more fully explained, tosupply a potential varying as the position of gate valve 92 is altered,and approximating Zero when the valve is just closed. A variableresistor R2 is connected for adjustment in response to displacement ofrebalancing servomotor 82, as schematically shown, for a purposehereinafter explained.

Referring now to Figure 1 of the drawing, it will be noted that weightsensing devices S. 1 and S. 2 each cornprises a differential transformerof which the primary winding is energized from an A. C. source bytransformer 103, as is also potentiometer R1. Sensing device S. 1,hereinafter referred to as the initial sensing device, is used only inthe net weighing system, for the primary purpose of energizingrebalancing servomotor 82 to cornpensate for variation in weight of thecontainer; sensing device S. 2 and potentiometer R1 deliver potentialswhich may be applied in opposed phase relation to energize the controlvalve servomotor 100 to effect the delivery to the container of anaccurately measured quantity of material by displacement of Vgate valve92. The physical connections of the several components, illustrated inFigure 2, are represented schematically in Figure 1. The energy outputof sensing devices S. 1 and S. 2, with each of which is associated aconventional balancing network, together with the energy output ofpotentiometer R1, is supplied to switching relay RL1 which, whende-energized,

transmits to a servo control amplifier, lhereinafter described, theOutput of initial weight sensing device to S. 1, and which, whenenergized, transmits to the same amplifier the outputs of final weightsensing device S.2 and potentiometer R1. The following brief descriptionof the principal elements of the amplifier, which is largelyconventional, should suce for an understanding of its function.

The output voltage from the selected sensing device S. 1 or S. 2,hereinafter called an error signal voltage, is applied by relay RLlthrough a step-up input transformer to the grid of cathode follower,tube V1. The arnplified error signal Voltage obtained from the output ofvacuum tube V1 is applied to the input of vacuum tube V2. Vacuum tube V2is an amplitude limiter and is used to limit the selected error signalvoltage to a maximum amplitude equal to that provided by potentiometerR1 when the gate valve 92 is in the wide open position. The signal fromvacuum tube V2 and the output from potentiometer R1 when the errorsignal is derived from sensing device S. 2) are applied, respectively,to resistors R19 and R20 of a mixer circuit network comprising resistorsR19, R20 and R21. The output of the mixer network is applied to the gridof vacuum tube V3. Vacuum tubes V3, V4, V5, V6 and V7 with associatedcornponents comprise a conventional servo amplifier. The output voltageobtained from the servo amplifier is switched by relay RLI either to therebalancing servomotor 82 (when sensing device S. 1 is operative) or tothe control valve servomotor 100 (when sensing device S. 2 andpotentiometer R1 are operative).

The amplied error signal voltage obtained from vacuum tube V1, describedabove, is also applied to the input tube V8 of a switching controlamplifier. Vacuum tube V8 is an amplitude limiter used to preventoverloading of the control amplifier. The signal from the output ofvacuum tube VS is applied to the grid of vacuum tube V9. Vacuum tubesV9, V10, and V11 comprise a conventional amplifier with a center tappedprimary output transformer 106. The signal from the secondary of theoutput transformer may be used to power an error meter 107, if desired.The signal from either side of the center tapped primary of the controlamplifier output transformer (points B and C) is applied to the grids ofthyratron tubes V12, V13, V14 and V15, which are employed to effectsequential operation of various switching relays, hereinafter described.

In the net weighing operation, the phase of the output from sensingdevice S. 1 is determined by the relative weights of the empty containeron the platform and the empty container weighed and filled in theimmediately preceding operation, so that the rebalancing sem/ometer 82is energized to run in the proper direction, the correction beingeffected in one direction if the empty container is of less weight, andin the opposite direction if the container is of greater weight than thecontainer immediately preceding. Stated otherwise, the change from anover-weight voltage to an under-weight voltage results in a phasereversal of the output of sensing device S. 1 the container being eitherover-weight or under-weight as compared with the immediately precedingcontainer.

The error voltage from either weight sensing device is amplified withoutphase shift by the switching control amplifier, and the amplifiercircuit is so designed that the output voltage between A and O is heldby tube VS to a constant value for input error voltages in excess of arelatively low predetermined level, and is either in phase or 180 out ofphase with the voltage between E and O.

The primary winding center tap of the switching control amplifier outputtransformer 106 is at ground potential for alternating current voltages.A high voltage must be obtainable between B and O and between C and O.The circuit is arranged so that the voltage between B and O is in phasewith the voltage between E and O for over-weight error input voltagesand 180 out of phase with the voltage betweei E and O for under-weighterror input voltages. The voltage between C and O is always 180 out ofphase with the voltage between B and O, due to transformer action. Thevoltage between B and O is connected through protective resistors to thecontrol grids of thyratron tubes V12 and V14. The voltage between C andO is connected through protective resistors to the control grids ofthyratron tubes V13 and V15.

Thyratrons V12 and V13 are operated with zero bias voltage and are usedinitially to detect the completion of the rebalancing cycle and linallyto detect completion of the material filling cycle. Thyratrons V14 andV15 are operated with a cathode bias voltage, preselected by adjustingresistor RSS, and are used to prevent recycling of the packaging controlin the event the empty container is above or below the preset Weightlimits, as hereinafter described in more detail. It the container iswithin the desired preset weight limits, the above mentioned cathodebias voltage prevents thyratrons V14 and V15 from conducting. Currentconduction by the thyratrons energizes their respective relays, theoperation of which will now be discussed.

The schematic diagram of Figure 1 illustrates the condition of the relaycontacts with all power oi. With no plate power supplied to the system,with the electron tube heater elements hot and with A. C. power on theplates of the thyratrons, the coil of relay RLS is de-energized; thecoil of relay RLS is energized; the coil of relayl RL9 is energized andthe coils of all other relays are de-energized.

With all power supplied, and with the weighing device balanced for theWeight of an average weight empty container, and with the platform ofthe weighing device empty, the coil of relay RL1 is de-energized; thecoil of relay RL2 is energized; the coil -of relay RL3 is de-energized;the coil of relay RL4 is de-energized; the coil of relay RLS isenergized; the coil of relay RL6 is de-energized; the coil of relay RL7is de-energized; the coil of relay RLS is de-energized; and, the coil ofrelay RL9 is energized. Thyratrons V13 and V15 are conducting.

If the cycling switch, push button P. B. 1, is closed .at this time,nothing happens because thyratron V15 is conducting, energizing the coilof relay RLS.

With an empty container weighing less than the weight of an averageweight container, but within the preselected weight tolerance determinedby variable resistor RSS, positioned on the receiving platform of theweighing device, the coil of relay RL1 remains tie-energized; the coilof relay RL2 remains energized; the coil of relay RL3 remainsde-energized; the coil of relay RL4 remains deenergized; thyratron V15becomes nonconducting, which de-energizes the coil -of relay RLS; thecoil of relay RL6 remains de-cnergized; the coil of relay RL7 remainsdeenergized; the coil of relay RLS remains de-energized; and the coil ofrelay RL9 remains energized. The control can be recycled since the coilof relay RLS is deenergized.

If the cycling switch P. B. 1 is closed at this time, the coil of slowopening relay RL4 energizes. Relay RL4 then remains energized becausecurrent continuity has been established through contacts B-C of relayRLS, through holding contacts A-B of relay RL4, and through contacts B-Cof relay RLS, completing the circuit to ground.

The energization of relay RL4 also closes contacts D--E of relay RL4,thereby completing a circuit through the coil of relay RL3. Relay RL3becomes energized. Since the coil of relay RL7 is de-energized when thecontacts D-E of relay RL4 close, a circuit is completed through contactsE-F of relay RL7 and through the coil of slow opening relay RL6,energizing relay RL6. Relay RL3 remains energized by the continuityestablished 6 through the closed contacts A-B of slow opening relay RL6.

The energization of either relay RL3 or relay RL4 deenergizes relay RL2,since contacts E-F of relay RL4 or contacts B-C of relay RL3 are broken,and hence the circuit through the coil of relay RL2 is broken. Thendeenergization of relay RL2 opens the circuit of ready signal 109(closed at the termination of the previous filling cycle), and disablesthe cycling circuit completed through cycling switch P. B. 1.Thereafter, any random or inadvertent use of the cycling switch P. B. 1will not influence the filling cycle.

Energizing relay RL3 removes the ground from the output signal of vacuumtube V2 in the servo control ampliiier. Since the weight of the emptycontainer is less than that of an average container in thisillustration, the initial weight sensing device S. 1 produces anunderweight error signal. The signal is amplified and applied to thecontrol phase of the rebalancing servomotor 82 through relay contactsB-C of denergized relay RL1. The signal causes the rebalancingservomotor to run in a direction to reduce the unbalance of the weighingdevice caused by the under-weight of the empty container. The unbalanceerror signal from the sensing device S. 1 is reduced.

When the error signal has been reduced to zero, i. e., when the outputvoltage of the initial weight sensing device S. 1 equals zero, thyratronV12 conducts, energizing relay RLS. Contacts B-C of relay RLS are brokenwhen relay RLS becomes energized and since relay RL9 was energized,opening contacts B-C of relay RL9, the ground on the coil of slowopening relay RL4 is removed. Relay RL9 is responsive to anyunder-Weight conditions.

When an over-weight container, within the preselected limits, is placedon the platform of the weighing device, with the weighing devicebalanced for the weight of an average weight container, relay RLSbecomes energized and relay RL9 is denergized. If the cycling switch P.B. 1 is closed, the initial weight sensing device S. 1 produces anover-weight error signal. The signal runs the rebalancing servomotor 32in a direction to reduce the lack of balance occasioned by theover-weight empty container, as in the operation described above.

If an empty container equal in weight to an average weight emptycontainer is placed on the platform with the weighing device balancedfor the weight of an average container, a zero error signal will beobtained from the initial weight sensing device S. 1. Thyratron V12 andthyratron V13 will conduct, energizing relay RLS and relay RL9. If thecycling switch P. B. 1 is closed at this time, the coil of slow openingrelay RL4 energizes as generally described above. The holding circuit ofrelay RL4 is open, since the paralleled contacts B-C of relay RLS andrelay RL9 are open. Relay RL4, after a brief time delay, determined bythe slow opening circuit of relay RL4, may now reopen. While relay RL4is closed, the rebalancing servomotor 82 does not run because the errorsignal from the initial Weight sensing device S. 1 is zero.

The condition of all relay contacts immediately prior to de-energizationof the coil of relay RL4, representing completion of the empty containerrebalancing cycle for purposes of net weight filling is as follows:Relay RL1 is de-energized; relay RL2 is de-energized; relay RL3 isenergized; relay RL4 is energized; relay RLS is de-energized; relay RL6is energized; relay RL7 is de-energized; relay RLS is energized, andrelay RL9 is energized.

If a container having a weight under the desired preselected weightlimits of an average weight container, as preset by means of resistorR58, is placed on the platform of the weighing device, the control willnot cycle when P. B. 1 is closed because thyratron V1S will conduct,energizing relay RLS. The condition of the relays under suchcircumstances is as follows: Relay RL1 is de-energized; relay RL2 isenergized; relay RL3 is de-energized, relay RL4 is de-energized; relayRLS is energized; relay V1.3 and V are conducting. To permit cycling, acontainer within the desired weight limits must be placed on theplatform of the weighing device.

If a container whose Weight is over the desired preselected weightlimits of an average weight container, as

preset by means of resistor R58, is placed on the platform of theweighing device, the control will not cycle when P. B. 1 is closedbecause relay RL5 is energized. The condition of the relays under suchcircumstances is as follows: Thyratron V12 is conducting, thyratron V14is conducting, relay RL1 is de-energized; relay RL2 is energized; relayRLS is de-energized; relay RL4 is de-energized; relay RLS is energized;relay RL6 is de-energized; relay RL7 is cie-energized; relay RLS isenergized; and relay RL9 is de-energized. To permit cycling, a containerwithin the desired weight limits must be placed on the platform of theweighing device.

The foregoing description of the net weighing operation assumes that theweighing device is initially balanced for the weight of an averageweight empty container. However, upon the conclusion of net weighing andfilling operations in which the container, although within thepermissible tolerance is not of average weight, thevariation of thecontainer weight from the average has been compensated by tensioning orrelaxing spring S0, and it is obviously undesirable to require theoperator to restore the normal balance before weighing and filling thenext succeeding container. Thus if a container is of less than averageweight, spring Sti is tensioned by rebalancing servomotor 82 during thenormal net weighing operation. Then if the succeeding container is ofmore than average weight, although within the permissible tolerance, itmay nevertheless result in the transmission of an error signal fromsensing device S. 1 of suiiicient magnitude to render V14 conducting;whereby relay RLS is energized to prevent further cycling. To avoidthis, variable resistor R2, mechanically coupled to rebalancingservomotor 82, is automatically adjusted Vduring the preceding netweighing operation to supply a correcting bias to thyratrons V14 andV15' of the sense and magnitude required to compensate for theoff-balance condition of the weighting device.

As soon as relay RL4 is de-energized, the filling cycle is initiated asfollows: When relay RL4 is de-energzed, contacts E--F of relay RL4 areclosed, thereby supply- -ing power through the closed contacts A--B ofrelay RLS, which is energized, to the coils of relays RL1 and RL7. RelayRL1 is energized. Relay RL-3 remains energized since power is suppliedto the coil of relay RLS through the closed contacts A-B of the slowopening, already energized relay RL6. Relay RL6 is maintained in anenergized condition by power supplied to the coil of relay RL6 throughrelay contacts E-F of deenergized relay RL7 and relay contacts A-B ofrelay RL6.

When relay RL1 becomes energized, the inputs of the servo and controlamplifiers are transferred from the initial weight sensing device S. 1,to the final weight sensing device S. 2. The output of the servoamplifier is also transferred from the rebalancing servomotor 82 to thecontrol valve servomotor 100. The potentiometer R1 is connected to theservo amplifier.

The error signal from the final weight sensing device S. 2 is amplifiedby the switching control amplifier, causing thvratrons V13 and V15 tofire and extinguishing thyratron V12. Relay RLS energizes, relay RLSdeenergizes, and relay RL9 energizes.

When relay RLS is de-energized, contacts E-F thereof close, therebycompleting the circuit to the coil of relay RL7. Relay RL7 is energized.When slow opening relay RL7 is energized, the power to the coil of slowopening relay RL6 is removed by breaking contacts E-F valve.

S of relay RL7. Relay RL7 has now taken over the function of relay RL6in holding relay RLclosed.

As soon as relay RL1 is energized, the error signal from the finalweight sensing device S. 2 is amplified by the servo control amplifierand applied yto the control valve servomotor 100. The error signalcauses motor 100 to run in a direction to open the material control Whenthe material control valve 92 opens, the filling material flows into theempty container 71.

At this instant, the conditions of the relays are as follows: Relay RL1is energized; relay RL2 is de-energized; relay RL3 is energized; relayRL4 is cle-energized; relay RLS is energized; relay RL6 is de-energized;relay RL7 is energized; rel-ay RLS is de-energized; relay RL9 isenergized, thyratron V12 is nonconducting; thyratron V13 is conducting;and, thvratron V15 is conducting.

The control valve servomotor 100 continues to run, increasing theopening .of valve 92 until the voltage output of potentiometer R1,applied to the grid of vacuum tube V3, has reached a value equal to theamplitude limited error signal voltage of the final weight sensingdevice S. 2, also applied to the grid of vacuum tube V3. Since these twovoltages are 180 out of phase and of equal amplitude, they cancel eachother, resulting in a zero servo amplifier output. The control valve 92has then reached its maximum open position, preselected 'by appropriateadjustment of the value of resistor R15.

The filling operation continues at this maximum rate until the errorsignal voltage from the final weight sensing device S. 2, controlled byresistor R13, falls to a value which will no longer be limited by vacuumtube V2. When the error signal falls below the limiting value,representing about filling of the container, the amplitude of the outputfrom the follow-up potentiometer results in an unbalanced voltage at thecontrol grid of vacuum tube V3. The unbalanced voltage is amplified inthe servo amplifier, causing the control valve servomotor to initiateclosing of valve 92.

When the error signal from the nal weight sensing device S. 2 hasreached zero, i. e., when the output voltage of the variable lineartransformer equals zero, the control valve 92 will be in an initialcut-off position predetermined by the setting of control resistor R61.The predetermined initial cut-off position of the control valve stopsmaterial flow. Thyratron V12 conducts, energizing relay RLS. Theenergization of relay RLS shorts resistor R60 by closing contacts D-Ethereof. The snorting of resistor R60 advances the zero output positionof potentiometer R1, causing the control valve servomotor to close thematerial control valve beyond cut-off. The breaking of contacts E-F ofrelay RLS removes the power from the coil of slo-w opening relay RL7,permitting it to de-energize and lock the control valve and otherwise toreset the system for the next succeeding weighing cycle. Before thecontrol valve is looked, a time interval is provided to permit thecontrol to sense whether the container has the `desired weight, and topermit reopening of the material control valve should the containerweight be improper due to erratic flow of filling material, for example.

The de-energization of relay RL7 closes contacts B- C, which also shortcircuits resistor R60 to maintain the material control valve at itsposition beyond cut-ofi even though relay RLS may later becomecle-energized. When relay RL7 is de-energized, contacts D-E are broken,removing the power from the coil of relay RL3 and permitting it tode-energize. When relay RL3 is de-energized, contacts E-F are closed anda ground is placed on the output ofthe limiting amplifier V2. ContactsA-B of relay Rie-3 are also broken, removing the power to relay RL1 andpermitting it to de-energize. At the same time, contacts B-C of relayRL3 make contact, applying power to the coil of relay RLZ to energizethe latter, thereby closing the circuit through ready signal 109, toinform the operator of the completion of lling.

When relay RL1 is de-energized, the inputs of the control and servoamplifiers are switched to the initial weight sensing unit S. 1. Sensingunit S. 1 is then providing a high output voltage because of the heavyweight of the filled container on the platform. The error voltage isamplified by the switching control amplifier and is of such a phaserelationship that thyratron V14 conducts, energizing relay RLS which has`tie-energized during the normal filling cycle. Thyratron V12 continuesto conduct, maintaining relay RL8 in an energized condition.

.The condition of all relays at the completion of the filling cycle isas follows: Relay RL1 is de-energized; relay RL2 is energized; relay RL3is de-energized; relay RL4 is ide-energized; relay RLS is energized;relay RL6 is de-energized; relay RL7 is de-energized; relay RL8 isenergized and relay RL9 is de-energized.

The ready signal is established, but closing the cycling switch P. B. 1will not recycle the control because relay RLS is energized. As soon asthe filled container is replaced with an empty container within thepreselected weight limits, the control may be recycled by closingcycling switch P. B. 1. The successive balancing and filling cycles areidentical with the complete cycle outlined above.

The preceding discussion describes the entire operational cycle of theweighing and packaging control for an underweight container within thepreselected weight limits. A similar operational cycle is effected inthe instance of an overweight container within the preselected weightlimits or a container equal in weight to the average weight container,with the indicated modifications.

The operation of the device will now be described by reference to theessential components of the system, omitting reference where possible todetails of the amplifier circuits and switching relays in the interestof simplification.

In the initial adjustment of the mechanism, an empty container ofstandard weight is placed on platform 70, the tension on spring 80 isadjusted to bring the platform to a desired level, for instance, inalignment with an adjacent table or conveyor, whereupon a coarseadjustment of the weight sensing device S. 1 is effected by shifting rod88 vertically on arm 85, thereby to adjust S. 1 so that its output isapproximately zero. Final adjustment to this end may be effected byvarying resistor R4. Variable resistor R58 may then be adjusted toestablish the range of weight tolerance for the empty container.

Initial adjustment of weight sensing device S. 2 is then effected byfilling the standard container with the required amount by weight of thematerial, and displacing rod 89 with respect to arm 86 until the outputof weight sensing device S. 2 is reduced approximately to zero, finaladjustment to zero output being effected by varying resistor R7. Meterreadings may, of course, be taken to determine when zero output isreached.

Assuming that the ready signal 109 has been rendered operative at theconclusion of a net weighing and filling operation, the operator removesthe lled container, places an empty container on scale platform 70, andactuates switch P. B. 1. Weight sensing device S. 1 thereupon emits asignal of which the magnitude and phase are determined by the differencein weight between the conrainer on the platform and the empty containerpreviously dealt with. Automatic adjustment of the bias on thyratronsV14 and V15 is effected by variable resistor R2 as hereinbeforeexplained, so that as applied to these thyratrons, the magnitude of thesignal from S. 1 is representative of the difference in weight betweenthe container on the platform and a standard container. If thisdifference falls outside of the permissible tolerance, as determined bythe initial adjustment of variable resistor R58, then relay RLS isenergized to block further operation of the mechanism until thecontainer is replaced by one falling within the prescribed limits.

Rebalancing servomotor 82 is now operated by the sig nal from the servocontrol amplifier to an extent and in a direction determined-by themagnitude and phase of the output of weight sensing device S. 1 untilthe platform, and the container supported thereon, are displaced to theposition occupied by the platform after the initial adjustment of themechanism as hereinbefore described. When this position is reached,relay RL1 is energized to remove weight sensing device S. 1 andrebalancing servornotor 82 from the circuit and to introduce weightsensing device S. 2, potentiometer R1, and control valve servornotor100. The signal from S. 2 is now at a maximum value, and the signal fromR1 at a minimum value, and motor 100 will therefore be energized by theoutput of the servo control amplifier to displace gate valve 92 to thefully opened position. Since in the fully opened position of valve 92the signal produced by the potentiometer R1 is equal in magnitude to thesignal from weight sensing device S. 2, as limited by tube V2, thecontrol valve servornotor 100 will be de-energized. Rapid filling of thecontainer follows until a selected percentage, for instance about of therequired amount of material has been charged into the container, and thesignal resulting from weight sensing device S. 2 has fallen to the limitimposed by the servo control amplifier.

When the initial rapid filling phase of the cycle has been completed andthe signal from S. 2 begins to fall below the limiting value imposed bythe circuit, and below the value of the signal from potentiometer R1,servomotor will be energized to initiate closing movement of valve 92.During the closing movement of the valve, the continued discharge of thematerial into the container further reduces the signal from S. 2, butsince the signal from potentiometer R1 is concurrently reduced due tovalve movement toward closed position, the difference between the twopotentials remains small. If there be any irregularity in flow of thematerial into the container, or any inertia effect as the result of thefalling of irregularly size-d particles, the position of the scaleplatform may momentarily differ from the correct position. There is thena corresponding variation in the voltage output of S. 2 relative to thevoltage output of R1, and the valve movement is either accelerated orretarded momentarily. If, as a result of this uctuation in the voltages,they become momentarily equal, the energization of the valve motor willbe interrupted or, in the event the voltage from R1 momentarily becomesless than that from S. 2, the motor will be reversely energized, and ineither event, the movement of the valve toward the closed position isretarded. Consequently, there is a control and adjustment of fiow duringthe movement of the valve, which becomes increasingly important as theinitial cut-off position of the valve is approached, since there is animmediate response to irregularity in the delivery of material.

It may happen that when the initial cut-off position of the valve isreached, the precise amount of material required has not been delivered,due to irregular flow of the last increment of material, but that therelay RL8 has been energized by the momentary reduction to zero of thevoltage from S. 2, to effect displacement of the valve toward the beyondcut-off position, and that thereafter the platform acquires a positiontruly representative of the weight of material in the container and asmall voltage is thus developed at S. 2. The application of this voltageto thyratron V12 again de-energizes relay RL8, and the control valveservornotor is rotated in the reverse direction to open the valveslightly and thus to admit the limited quantity of material required toreduce the output of S. 2 again to zero. Thereupon the relay RL8 isagain energized, and an additional voltage is supplied to the controlvalve servornotor to displace the valve to the beyond cut-off position.Thus the sensing of irregular flow or incomplete filling may occur atany stage in the cycle subsequent to the initial major portion of thecycle, for the purpose of effecting immediate correction of such 11irregularity or incomplete filling, up toY the time the system functionsto lock the control valve in the beyond cutoff or final position, toreset the circuit for the next operation, and to energize the readysignal 109.

Itwill be appreciated that the inventive concept described and definedherein may be readily incorporated with automatic carton feed mechanismsof conventional type, whereby filled cartons are removed and replaced byempty cartons, and whereby the intervention of an operator is' madeunnecessary. Thus the initiation of the net weighing 'and filling cyclesmay be effected in response to the positioning by automatic means ofempty containers on the scale platform, off-size containers beingremoved automatically in response to operation of conventional circuitsenergized from relay RLS.

Again, while the invention is described, for convenience, by referenceto feed mechanism especially adapted to Vthe control of owable material,it is equally applicable to the handling of material which requirespositive feeding, for instance, by a screw conveyor or the like, thepotentiometer R1 being replaced by a voltage generator such as atachometer, constructed to deliver an output proportioned to theconveyor movement. Various other changes in the design and function ofthe equipment to adapt it to a wide variety of uses will readily occurto one skilled in the art.

Turning now to Figure 3, which illustrates the application of certainfeatures of the invention to a gross weighing system, .it will beobserved that the essential difference between Figures 1 and 3 is therestriction of the latter to those components peculiar to the grossweighing operation, and similar reference characters are employed inthese figures to identify essentially similar components in order toeliminate unnecessary duplication of descriptive matter.

YThus the gross weighing system omits the initial weight sensing deviceS. 1, the rebalancing servomotor 82 and the relays RL1, RL2, RL3, RL4,RLS, and RL6. Certain of the functions of the omitted relays areperformed by relay RL7 of Figure 3, including the disabling of the servocontrol amplifier and the energization of the ready signal at the closeof the filling operation. Again, the starting switch P. B. 1 is incircuit with switch contacts 'in switching relays RLS and RL9. Only onethyratron V12 is employed, its primary function being the termination ofthe filling operation when the output signal from S. 2 reaches zero, byenergization of relay RL9. The amplifiers of Figure 3 and Figure l aresubstantially identical.

The mode of operation of the system shown in Figure 3 is essentiallythat described hereinbefore in connection with the filling operationperformed by the system of Figure l, the initial weighing of thecontainer and the rebalancingV of the platform being eliminated. It isassumed, in the operation of the gross weighing system of Figure 3, thatthe containers are sufciently close in Weight to the standard containerto avoid the need for compensating correction, and to the extent thatcontainers depart .in weight from the standard, the system is inherentlyless accurate than the net weighing system hereinbefore described. Itpossesses, however, the decided advantage of proportional filling, thematerial being deliver'ed to the container with the accuracy which flowsfrom the use of the filling cycle hereinbefore described. The grossWeighing system is, of course, considerably simpler and therefore lessexpensive than the net weighing system, and is therefore more desirablefor many uses. lt is, of course, useful in -delivering a measuredquantity of material directly to a scale platform or pan when filling ofa container is not desired.

The schematic diagram of Figure 3 illustrates the condition of the relaycontacts with all power ofi". With no plate power supplied tothe system,with the electron tube heater elements hot and with A. C. power on theplates of the thyratron, the coil of relay RL7 is de-energized;

Y Y 12 Y the coil of relay RLS is de-energized; and the coil of relayRL9 is energized. Thyratron V12 .is conducting.

With all power supplied, and with an empty container positioned 0n thereceiving platform of the weighing device, the error signal from theweight sensing device S. 2 is amplified by the switching controlamplifier, causing thyratron V12 to become nonconductive. Relay RL9 isde-energized.

If the cycling switch P. B. 1 is closed at this time, the coil of slowopening relay RLS energizes. Relay RLS then remains energized becausecurrent continuity has been established through contacts B-C or relayRL9 and through holding contacts A--B of relay RLS, completing thecircuit to ground.

The energization of relay RLS also closes contacts VD---E of relay RLS,thereby completing a circuit through the coil of relay RL7. Relay RL7becomes energized.

As soon as relay RL7 is energized, the error signal from the weightsensing device S. 2 is amplified by the servo amplifier and applied tothe control valve servomotor 100. The error signal causes control valveservomotor 100 to run in a direction to open the material control valve92. When the material control valve 92 opens, the filling material flowsinto the empty container. At this instant relay RL7 is energized, relayRLS is energized, and relay RL9 is de-energized. Thyratron V12 isnonconductive.

The control valve servomotor 100 continues to run, increasing theopening of material control valve 92 until the voltage output ofpotentiometer R1, applied to the grid of vacuum tube V3, has reached avalue equal to the amplitude limited error signal voltage of the weightsensing device S. 2, also applied to the grid of vacuum tube V3. Sincethese two voltages are 180 out of phase and of equal amplitude, theycancel each other, resulting in a zero servo amplier output. Thematerial control valve 92 has then reached its maximum open position,preselected by appropriate adjustment of the value of resistor R15.

The filling operation continues at this maximum rate until the errorsignal voltage from the weight sensing device S. 2, controlled byresistor R13, falls to a value which will no longer be limited by vacuumtube V2. When the error signal falls below the limiting value,representing about filling of the container, the amplitude of the outputfrom the follow-up potentiometer results in an unbalanced voltage at thecontrol grid of vacuum tube V3. The unbalanced voltage is amplified inthe servo amplifier, causing the control valve servomotor to initiateclosing of material control valve 92.

When the error signal from the weight sensing device S. 2 has reachedzero, i. e., when the output voltage of the linear variable differentialtransformer equals zero, the material control valve 92 will be in aninitial cut-ofi position predetermined by the setting of controlresistor R61. The predetermined initial cut-Off position of the controlvalve stops material fiow. Thyratron V12 conducts, energizing relay RL9.The energization of relay RL9 shorts resistor R60 by closing contact A-Bthereof. The shorting of resistor R60 advances the zero output positionof potentiometer R1, causing the control valve servomotor to close thematerial control valve beyonnd cut-ofi. The breaking of contacts B-C ofrelay RL9 removes the power from the coil of slow opening relay RLS,permitting it to de-energize and lock the control valve in the beyondcut-off position. Before the control valve is locked, a time interval isprovided to permit reopening of the material control valve should thecontainer weight be improper due to erratic flow of filling material,for example.

The de-energization of relay RLS closes contacts E-F, which also shortcircuits resistor R60 to maintain the material control valve at itsposition beyond cut-ofi? even though relay RL9 may later becomede-energized. When relay RLS is de-energized, contacts D-E are broken,

removing the power from the coil of relay RL7 and permitting it tode-energize. When relay RL7 is de-energized, contacts BC are closed anda ground is placed on the output of the limiting amplifier V2. At thesame time, contacts E-F of relay RL7 make contact, thereby closing thecircuit through ready signal 109, to inform the operator of thecompletion of filling.

Having thus described the invention, what is claimed a new and desiredto be secured by Letters Patent is:

l. In apparatus for automatically delivering to a container apredetermined amount by weight of material, the combination with a scaleplatform adapted to receive a container, of balancing means supportingsaid platform for vertical displacement by the weight of the receivedcontainer, material feeding means positioned to discharge material intosaid container, control means actuated upon predetermined displacementof said platform by the charged container to terminate operation of saidmaterial feeding means, devices responsive to displacement of saidplatform by a received container having a weight falling outside apredetermined range of weights for preventing operation of said materialfeeding means, and means responsive to displacement of said platform bya received container having a weight falling within said predeterminedrange for restoring said platform with the container thereon, prior tooperation of said material feeding means, to a predetermined positionregardless of deviation of the container weight from a predeterminedaverage container weight within said range.

2. In apparatus for automatically delivering to a container apredetermined amount by weight of material, the combination with a scaleplatform adapted to receive an empty container, of balancing meanssupporting said platform for vertical displacement by the weight of thereceived container, material feeding means positioned to dischargematerial into said container, devices responsive to displacement of saidplatform by a received container having a weight falling outside apredetermined range of weights for preventing operation of said materialfeeding means, and means responsive to displacement of said platform bya received container having a weight falling Within said predeterminedrange, but deviating from a predetermined average container weightwithin that range, for restoring said platform with the containerthereon, prior to operation of said material feeding means, to apredetermined position regardless of the deviation of the container fromthe average weight, and control means operable automatically onrestoration of said platform to said predetermined position forinitiating and terminating operation of said material feeding means.

3. In apparatus for automatically delivering to a container apredetermined amount by weight of material, the combination with a scaleplatform adapted to receive a container, balancing means supporting saidplatform for vertical displacement by the weight of the receivedcontainer, material feeding means positioned to discharge material intosaid container, control means operable to initiate operation of saidmaterial feeding means, said control means being responsive todisplacement of said platform to a predetermined position by the chargedcontainer to terminate operation of said material feeding means, anddevices responsive to displacement of said platform by a received emptycontainer only when the container falls within a predetermined range ofweights for restoring said platform with the container thereon to apredetermined position regardless of deviation of the container withinsaid range, and thereafter rendering said control means operative toinitiate operation of said feeding means.

4. In apparatus for automatically delivering to a container apredetermined amount by weight of material, the combination with a scaleplatform, of balancing means yieldably supporting said platform forvertical displacement, material feeding means positioned to dischargematerial onto said platform, and control means for said feeding meansautomatically operable to (a) initiate withdrawal ofmaterial at amaximum rate during the first and major portion of the feeding cycle,(b) progressively reduce the rate of withdrawal of material to zeroduring the latter portion of the feeding cycle, and (c) vary the rate ofprogressive reduction of withdrawal of material upon the occurrence ofirregular feed of material at any point in the feeding cycle subsequentto the first and major portion thereof to minimize the effect ofirregular feed.

5. In apparatus for automatically delivering to a container apredetermined amount by weight of material, the combination with a scaleplatform, of balancing means yieldably supporting said platform forvertical displacement, material feeding means positioned to dischargematerial onto said platform, and control means for said feeding meansautomatically operable to (a) initiate withdrawal of material at amaximum rate during the first and major portion of the feeding cycle,(b) progressively reduce the rate of withdrawal of material to zeroduring the latter portion of the feeding cycle, and (c) thereafterreinitiate withdrawal of material to compensate for a deficiency in thetotal amount by weight of material fed.

6. In apparatus for automatically delivering a predetermined weight offree flowing material from a source of supply, the combination with thesource, of material feed regulating means for withdrawing material fromsaid source, a motor, a driving connection between said motor and saidfeed regulating means to vary the rate of withdrawal of material betweenzero and a predetermined maximum rate, a scale platform receiving andbeing depressed by the withdrawn material, devices developing electricalsignals of a magnitude varying respectively with the height of saidscale platform and the rate of withdrawal of material from said source,and means combining said signals in opposed phase relation and applyingthe combined signal to control said motor to (a) initiate withdrawal ofmaterial at the maximum rate during the first and major portion of thefeeding cycle and (b) progressively reduce the rate of withdrawal ofmaterial substantially to zero during the latter portion of the feedingcycle.

7. In apparatus for automatically delivering a predetermined weight offree flowing material from a source of supply, the combination with thesource, of material feed regulating means for withdrawing material fromsaid source, a motor, a driving connection between said motor and saidfeed regulating means to vary the rate of withdrawal of material betweenzero and a predetermined maximum rate, a scale platform receiving andbeing depressed by the withdrawn material, devices developing electricalsignals of a magnitude varying respectively with the height of saidscale platform and the rate of withdrawal of material from said source,and means combining said signals in opposed phase relation and applyingthe combined signal to control said motor to (a) initiate withdrawal ofmaterial at the maximum rate during the first and major portion of thefeeding cycle, (b) progressively reduce the rate of withdrawal ofmaterial substantially to zero during the latter portion of the feedingcycle, and (c) reinitiate and thereafter terminate withdrawal of ameasured quantity of material representing the difference between thepredetermined weight of material to be delivered and the weight ofmaterial withdrawn prior to such reinitiation of withdrawal of material.

8. In apparatus for automatically delivering a predetermined weight offree flowing material from a source of supply, the combination with thesource, of a control valve for regulating withdrawal of material fromsaid source, a motor, a driving connection between said motor and saidvalve to vary the rate of withdrawal of material between zero and apredetermined maximum rate, a scale platform receiving and beingdepressed by the material withdrawn from said source, devices developingelectrical signals Varying respectively with the height of said scaleplatform and the rate of withdrawal of material from said source, andmeans combining said signals in opposed phase relation and applying thecombined signal to control said motor to (a) open said valve to initiatewithdrawal of material at the maximum rate during the rst and majorportion of the feeding cycle, (b) displace said valve gradually to aclosed position to progressively reduce the rate of withdrawal ofmaterial to zero during the latter portion of the feeding cycle, and (c)reopen and thereafter close said valve to reinitiate and again terminatewithdrawal of a measured quantity of material representing thedifference between the predetermined weight of material to be deliveredand the weight of material withdrawn prior to such reinitiation ofwithdrawal of material.

9. In apparatus for automatically delivering a predetermined weight offree owing material from a source of supply, the combination with thesource, of a control valve for regulating withdrawal of material fromsaid source, a motor, a driving connection between said motor and saidvalve to vary the rate of withdrawal of material between zero and apredetermined maximum rate, a scale platform receiving and beingdepressed by the material withdrawn from said source, devices developingelectrical signals varying respective'ly with the height of said scaleplatform and the rate of withdrawal of material from said source, andmeans combining said signals in opposed phase relation and applying thecombined signal to control said motor to (a) open said valve to initiatewithdrawal of material at the maximum rate during the first and majorportion of the feeding cycle, (b) displace said valve gradually to aclosed position to progressively reduce the rate of withdrawal ofmaterial to zero during the latter portion of the feeding cycle, andmeans automatically operable thereafter to develop a further signal andto apply said last named signal to control said motor to move said valvefurther and beyond said closed position to preclude unwanted withdrawalof material from said source.

10. In apparatus for automatically delivering a predetermined weight offree flowing material from a source of supply, the combination with thesource, of material feed Iregulating means for withdrawing material fromsaid source, a motor, a driving connection between said motor and saidfeed regulating means to vary the rate of withdrawal of material betweenZero and a predetermined maximum rate, a depressible scale platformreceiving the withdrawn material from said feeding means, devicesdeveloping electrical signals inversely proportioned respectively to theheight of said scale platform and to the rate of withdrawal of materialfrom said source, and means combining said signals in opposed phaserelation and applying the combined signal to control said motor to (a)initiate withdrawal of material and (b) progressively reduce the rate ofwithdrawal of material substantially to zero.

References Cited in the file of this patent UNITED STATES PATENTS2,067,743 Weckerly Jan. 12, 1937 2,351,606 Gold et al June 20, 19442,395,674 Lauterbach Feb. 26, 1946 2,548,473 Gregory Apr. 10, 1951

